Factors influencing the generation of murine dendritic cells from bone marrow: The special role of fetal calf serum

Guidelines for mouse and human DC generation

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various non-lymphoid tissues. This article provides protocols with top ticks and pitfalls for preparation and successful generation of mouse and human DC from different cellular sources, such as murine BM and HoxB8 cells, as well as human CD34+ cells from cord blood, BM, and peripheral blood or peripheral blood monocytes. We describe murine cDC1, cDC2, and pDC generation with Flt3L and the generation of BM-derived DC with GM-CSF. Protocols for human DC generation focus on CD34+ cell culture on OP9 cell layers for cDC1, cDC2, cDC3, and pDC subset generation and DC generation from peripheral blood monocytes (MoDC). Additional protocols include enrichment of murine DC subsets, CRISPR/Cas9 editing, and clinical grade human DC generation. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists.

GM-CSF, Flt3-L and IL-4 affect viability and function of conventional dendritic cell types 1 and 2

Conventional type 1 dendritic cells (cDC1) and conventional type 2 dendritic cells (cDC2) have attracted increasing attention as alternatives to monocyte-derived dendritic cells (moDCs) in cancer immunotherapy. Use of cDCs for therapy has been hindered by their low numbers in peripheral blood. In the present study, we found that extensive spontaneous apoptosis and cDC death in culture within 24hrs represent an additional challenge. Different media conditions that maintain cDC viability and function were investigated. CD141+ cDC1 and CD1c+ cDC2 were isolated from healthy blood donor buffy coats. Low viabilities were found with CellGenix DC, RPMI-1640, and X-VIVO 15 standard culture media and with several supplements at 24hrs and 48hrs. Among multiple factors it was found that GM-CSF improved both cDC1 and cDC2 viability, whereas Flt3-L and IL-4 only increased viability of cDC1 and cDC2, respectively. Combinations of these three cytokines improved viability of both cDCs further, both at 24hrs and 48hrs time points. Although these cytokines have been extensively investigated for their role in myeloid cell differentiation, and are also used clinically, their effects on mature cDCs remain incompletely known, in particular effects on pro-inflammatory or tolerogenic cDC features. HLA-DR, CD80, CD83, CD86, PD-L1 and PD-L2 cDC membrane expressions were relatively little affected by GM-CSF, IL-4 and Flt3-L cytokine supplements compared to the strong induction following Toll-like receptor (TLR) stimulation for 24hrs. With minor exceptions the three cytokines appeared to be permissive to the TLR-induced marker expression. Allogeneic mixed leukocyte reaction showed that the cytokines promoted T-cell proliferation and revealed a potential to boost both Th1 and Th2 polarizing cytokines. GM-CSF and Flt3-L and their combination improved the capability of cDC1 for dextran uptake, while in cDC2, dextran capture was improved by GM-CSF. The data suggest that GM-CSF, IL-4 and Flt3-L and combinations might be beneficial for DC viability and function in vitro. Limited viability of cDCs could be a confounding variable experimentally and in immunotherapy.

Flt3L, LIF, and IL-10 combination promotes the selective in vitro development of ESAMlow cDC2B from murine bone marrow

The development of two conventional dendritic cells (DC) subsets (cDC1 and cDC2) and the plasmacytoid DC (pDC) in vivo and in cultures of bone marrow (BM) cells is mediated by the growth factor Flt3L. However, little is known about the factors that direct the development of the individual DC subsets. Here, we describe the selective in vitro generation of murine ESAM^low CD103^- XCR1^- CD172a⁺ CD11b⁺ cDC2 from BM by treatment with a combination of Flt3L, LIF, and IL-10 (collectively named as FL10). FL10 promotes common dendritic cell progenitors (CDP) proliferation in the cultures, similar to Flt3L and CDP sorted and cultured in FL10 generate exclusively cDC2. These cDC2 express the transcription factors Irf4, Klf4, and Notch2, and their growth is reduced using BM from Irf4^-/- mice, but the expression of Batf3 and Tcf4 is low. Functionally they respond to TLR3, TLR4, and TLR9 signals by upregulation of the surface maturation markers MHC II, CD80, CD86, and CD40, while they poorly secrete proinflammatory cytokines. Peptide presentation to TCR transgenic OT-II cells induced proliferation and IFN-γ production that was similar to GM-CSF-generated BM-DC and higher than Flt3L-generated DC. Together, our data support that FL10 culture of BM cells selectively promotes CDP-derived ESAM^low cDC2 (cDC2B) development and survival in vitro.

CDCP1 on Dendritic Cells Contributes to the Development of a Model of Kawasaki Disease

The etiology and pathology of Kawasaki disease (KD) remain elusive. Cub domain-containing protein 1 (CDCP1), a cell-surface protein that confers poor prognosis of patients with certain solid tumors, was recently identified as one of the most significantly upregulated genes in SARS-CoV-2-infected children who developed systemic vasculitis, a hallmark of KD. However, a potential role of CDCP1 in KD has not previously been explored. In this study, we found that CDCP1 knockout (KO) mice exhibited attenuated coronary and aortic vasculitis and decreased serum Candida albicans water-soluble fraction (CAWS)-specific IgM/IgG2a and IL-6 concentrations compared with wild-type mice in an established model of KD induced by CAWS administration. CDCP1 expression was not detectable in cardiomyocytes, cardio fibroblasts, or coronary endothelium, but constitutive expression of CDCP1 was observed on dendritic cells (DCs) and was upregulated by CAWS stimulation. CAWS-induced IL-6 production was significantly reduced in CDCP1 KO DCs, in association with impaired Syk-MAPK signaling pathway activation. These novel findings suggest that CDCP1 might regulate KD development by modulating IL-6 production from DCs via the Syk-MAPK signaling pathway.

In Vitro Generation of Murine Myeloid-Derived Suppressor Cells, Analysis of Markers, Developmental Commitment, and Function

Myeloid-derived suppressor cells (MDSC) appear at relatively low frequencies in diseased organs such as tumors or infection sites, but accumulate systemically in the spleen. So far MDSC have been reported in humans and experimental animals such as mice, rats, and nonhuman primates. Therefore, methods to generate MDSC in large amounts in vitro can serve as an additional tool to study their biology. Here, we describe in detail the generation of murine MDSC with GM-CSF from bone marrow (BM). Both subsets of granulocytic (G-MDSC) and monocytic MDSC (M-MDSC) are generated by this cytokine. We provide panels of phenotypic markers to distinguish them from non-suppressive cells and define developmental stages of monocytes developing into M-MDSC by two subsequent steps in vitro.

Rotavirus VP6 Adjuvant Effect on Norovirus GII.4 Virus-Like Particle Uptake and Presentation by Bone Marrow-Derived Dendritic Cells In Vitro and In Vivo

We have previously shown that rotavirus (RV) inner capsid protein VP6 has an adjuvant effect on norovirus (NoV) virus-like particle- (VLP-) induced immune responses and studied the adjuvant mechanism in immortalized cell lines used as antigen-presenting cells (APCs). Here, we investigated the uptake and presentation of RV VP6 and NoV GII.4 VLPs by primary bone marrow-derived dendritic cells (BMDCs). The adjuvant effect of VP6 on GII.4 VLP presentation and NoV-specific immune response induction by BMDC in vivo was also studied. Intracellular staining demonstrated that BMDCs internalized both antigens, but VP6 more efficiently than NoV VLPs. Both antigens were processed and presented to antigen-primed T cells, which responded by robust interferon γ secretion. When GII.4 VLPs and VP6 were mixed in the same pulsing reaction, a subpopulation of the cells had uptaken both antigens. Furthermore, VP6 copulsing increased GII.4 VLP uptake by 37% and activated BMDCs to secrete 2-5-fold increased levels of interleukin 6 and tumor necrosis factor α compared to VLP pulsing alone. When in vitro-pulsed BMDCs were transferred to syngeneic BALB/c mice, VP6 improved NoV-specific antibody responses. The results of this study support the earlier findings of VP6 adjuvant effect in vitro and in vivo.

Rotavirus VP6 as an Adjuvant for Bivalent Norovirus Vaccine Produced in Nicotiana benthamiana

Rotaviruses (RVs) and noroviruses (NoVs) are major causes of childhood acute gastroenteritis. During development of a combination vaccine based on NoV virus-like particles (VLP) and RV VP6 produced in baculovirus expression system in insect cells, a dual role of VP6 as a vaccine antigen and an adjuvant for NoV-specific immune responses was discovered. Here the VP6 adjuvant effect on bivalent GI.4 and GII.4-2006a NoV VLPs produced in Nicotiana benthamiana was investigated. BALB/c mice were immunized intradermally with suboptimal (0.3 µg) dose of each NoV VLP alone or combined with 10 µg of VP6, or equal doses of NoV VLPs and VP6 (1 µg/antigen). NoV-specific serum IgG antibodies and their blocking activity were analyzed using vaccine-homologous and heterologous NoV VLPs. Immunization with 0.3 µg NoV VLPs alone was insufficient to induce NoV-specific immune responses, but with co-administration of 10 µg of VP6, antibodies against vaccine-derived and heterologous NoV genotypes were generated. Furthermore, corresponding adjuvant effect of VP6 was observed with 1 µg dose. Efficient uptake and presentation of VP6 by dendritic cells was demonstrated in vitro. These results show that adjuvant effect of VP6 on bivalent NoV VLP vaccine is independent of the cell source used for vaccine production.

Bone Marrow-Derived Dendritic Cells

Dendritic cells are a specialized type of antigen-presenting cell that bridges both innate and adaptive immune system function. While much is understood about dendritic cells and their role in the immune system, the study of these cells is critical to gain a more complete understanding of their function. The isolation and culture of dendritic cells from mouse tissues can be challenging, due in part to the low number of cells isolated. The following protocol outlines methods to optimize the isolation and culture of large numbers of dendritic cells from mouse bone marrow to facilitate a broad range of downstream experimental applications.

GM-CSF Culture Revisited: Preparation of Bulk Populations of Highly Pure Dendritic Cells from Mouse Bone Marrow

Dendritic cells (DC) loaded with specific peptides are strongly immunogenic for T cells and can be used for cancer immunotherapy. For immunogenic tumors such as melanoma, injection of autologous DC loaded with tumor cell extracts or peptides can induce tumor regression but in only a small proportion of patients. Nevertheless, recent studies on the efficacy of checkpoint blockade for boosting antitumor immunity plus advances in defining tumor neoantigens are stimulating renewed interest in DC immunotherapy. Despite intensive investigation, however, preparation of bulk populations of mature DC has proved difficult, and most preparations contain a significant proportion of potentially tolerogenic immature DC. In this study, we have modified the well-established GM-CSF culture system to prepare substantial quantities of highly pure (>95%) mature DC from mouse bone marrow cells and defined their progenitors. We show that obtaining high yields and purity of DC are heavily dependent on cell density in the cultures and the tempo of addition of growth and maturation stimuli. When loaded with specific peptide, the DC are strongly immunogenic for CD4 and CD8 T cells in vivo and elicit effective antitumor immunity.

Rapid cooling of rabbit embryos in a synthetic medium

Embryo cryopreservation media usually contain animal-derived products, such as bovine serum albumin (BSA). These products present two major disadvantages: an undefined variable composition and a risk of pathogen transmission. We aimed to evaluate the effect of replacing BSA in rabbit embryo rapid cooling "freezing" and warming media with a chemically defined medium with no animal-derived products: STEM ALPHA. Cryo3 ("Cryo3"). A total of 1540 rabbit morulae were divided into three cryopreservation groups (group 1: BSA, group 2: 20% Cryo3 and group 3: 100% Cryo3) and a fresh controls group. After rapid cooling, embryos were cultured (in vitro approach), or transferred into synchronized does (in vivo approach). In the in vitro approach, post-warm survival rates obtained with 100% Cryo3 (94.9%) were superior to BSA (90.8%) and 20% Cryo3 (85.6%). The blastocyst formation rate was similar between BSA, 20% Cryo3 and 100% Cryo3 groups (85.1, 77.9 and 83.3%, respectively), as was the expansion/hatching rate (63.1, 63.4 and 58.0%, respectively) and embryo mitochondrial activity. In the in vivo approach, pregnancy (80.0, 68.0 and 95.2%, respectively), implantation (40.5, 45.9 and 44.8%, respectively), and live-foetus rates (35.6, 35.5 and 38.1%, respectively) were similar between the three groups. To conclude, Cryo3 can replace BSA in rabbit embryo rapid cooling "freezing" and warming media.

Influence of various medium environment to in vitro human T cell culture

Nowadays, adoptive T cell immunotherapy is emerging as a novel and potent treatment for cancer. To prepare enough effective T cells for treatment use, their rapid expansion is favorable. Our study compared 6 commonly used cultural media for human T cells, including serum-containing media and serum-free media, namely RPMI 1640, IMDM, Gibco OpTmizer CTS T Cell Expansion SFM, Gibco AIM-V Medium CTS, LONZA X-VIVO 15, and StemSpan SFEM with or without Dynabeads Human T-Activator CD3/CD28, on in vitro T cell expansion, apoptosis, and immune phenotype. Our study results suggest that serum-free media provide better proliferation environment for T cells. Among the 3 serum-free media, we identify OpTmizer and AIM-V as better T cell culture environments compared with X-VIVO as T cells are proved to have higher viability in the first two media. Besides, we found that in vitro human T cells keep relatively resting status among non-CD3/CD28 groups, since they have weak proliferation and apoptosis abilities. The phenotypes of T cells in different cultural environments over time indicate T cells maturation during culture duration. These results provide a firm foundation of adoptive T cell immunotherapy.

Optimization of Ex Vivo Murine Bone Marrow Derived Immature Dendritic Cells: A Comparative Analysis of Flask Culture Method and Mouse CD11c Positive Selection Kit Method

12-14 days of culturing of bone marrow (BM) cells containing various growth factors is widely used method for generating dendritic cells (DCs) from suspended cell population. Here we compared flask culture method and commercially available CD11c Positive Selection kit method. Immature BMDCs' purity of adherent as well as suspended cell population was generated in the decreasing concentration of recombinant-murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) in nontreated tissue culture flasks. The expression of CD11c, MHCII, CD40, and CD86 was measured by flow cytometry. We found significant difference (P < 0.05) between the two methods in the adherent cells population but no significant difference was observed between the suspended cell populations with respect to CD11c+ count. However, CD11c+ was significantly higher in both adhered and suspended cell population by culture method but kit method gave more CD11c+ from suspended cells population only. On the other hand, using both methods, immature DC expressed moderate level of MHC class II molecules as well as low levels of CD40 and CD86. Our findings suggest that widely used culture method gives the best results in terms of yield, viability, and purity of BMDCs from both adherent and suspended cell population whereas kit method works well for suspended cell population.

GM-CSF Monocyte-Derived Cells and Langerhans Cells As Part of the Dendritic Cell Family

Dendritic cells (DCs) and macrophages (Mph) share many characteristics as components of the innate immune system. The criteria to classify the multitude of subsets within the mononuclear phagocyte system are currently phenotype, ontogeny, transcription patterns, epigenetic adaptations, and function. More recently, ontogenetic, transcriptional, and proteomic research approaches uncovered major developmental differences between Flt3L-dependent conventional DCs as compared with Mphs and monocyte-derived DCs (MoDCs), the latter mainly generated in vitro from murine bone marrow-derived DCs (BM-DCs) or human CD14⁺ peripheral blood monocytes. Conversely, in vitro GM-CSF-dependent monocyte-derived Mphs largely resemble MoDCs whereas tissue-resident Mphs show a common embryonic origin from yolk sac and fetal liver with Langerhans cells (LCs). The novel ontogenetic findings opened discussions on the terminology of DCs versus Mphs. Here, we bring forward arguments to facilitate definitions of BM-DCs, MoDCs, and LCs. We propose a group model of terminology for all DC subsets that attempts to encompass both ontogeny and function.

mRNA-based dendritic cell immunization improves survival in ret transgenic mouse melanoma model

Malignant melanoma is characterized by a rapid progression, metastasis to distant organs and resistance to chemo and radiotherapy. Although melanoma is capable of eliciting an immune response, the disease progresses and the overall results of immunotherapeutic clinical studies are not satisfactory. Recently, we have developed a novel genetic platform for improving an induction of peptide-specific CD8(+) T cells by dendritic cell (DC) based on membrane-anchored β2-microglobulin (β2m) linked to a selected antigenic peptide at the N-terminus and to the cytosolic domain of TLR4 at the C-terminus. In vitro transcribed mRNA transfection of antigen-presenting cells (APCs) resulted in an efficient coupling of peptide presentation and cell activation. In this research, we utilize the chimeric platform to induce an immune response in ret transgenic mice that spontaneously develop malignant skin melanoma and to examine its effect on the overall survival of tumor-bearing mice. Following immunization with chimeric construct system, we observe a significantly prolonged survival of tumor-bearing mice as compared to the control group. Moreover, we see elevations in the frequency of CD62L(hi)CD44(hi) central and CD62L(lo)CD44(hi) effector memory CD8(+) T-cell subsets. Importantly, we do not observe any changes in frequencies of regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) in the vaccinated groups. Our data suggest that this novel vaccination approach could be efficiently applied for the immunotherapy of malignant melanoma.

Dendritic cells combined with doxorubicin induces immunogenic cell death and exhibits antitumor effects for osteosarcoma

The effects of dendritic cells (DCs) with low dose doxorubicin on the enhancement of the systemic immune response, including the effects on calreticulin (CRT) expression, heat shock protein 70 (HSP70) on the cell surface expression, and the enhancement of high mobility group box 1 (HMGB1) release from cancer cells, remain unclear. The present study investigated whether the combination of DCs and doxorubicin (ADM) induces immune cell death, and leads to tumor growth inhibition in a murine osteosarcoma model. To evaluate immune response activation in vivo, 4 groups of mice were established: i) untreated mice, ii) DC-treated mice, iii) ADM-treated mice, and iv) DC and ADM-treated mice. Immunological cell death and CRT, HSP70, and HMGB1 expression levels were higher in doxorubicin-treated cells than those in untreated or those treated with DCs alone. NF-κB expression was higher in the DCs after ligand activation using CRT, HSP70, or HMGB1 in vitro. Mice treated with DCs and ADM displayed an increased number of CD8⁺ T-lymphocytes within metastatic tumors and inhibition of metastatic growth. The expression of CRT and the release of HMGB1 from tumor tissues were increased in the ADM-treated groups. Treatment with DCs and ADM resulted in the highest serum interferon-γ levels. Combining ADM, which can induce immunogenic cell death, with DCs enhanced the systemic immune response. The findings of the present study provide further support for the continued development of antitumor agents that induce cell death and the immune response to target osteosarcoma.

Dendritic cells combined with anti-GITR antibody produce antitumor effects in osteosarcoma

We attempted to enhance the antitumor effects of tumor lysate-pulsed dendritic cells by eliminating regulatory T cells. The combinatorial effects of dendritic cells and agonist anti-glucocorticoid-induced tumor necrosis factor receptor (anti-GITR) antibodies were investigated with respect to enhancement of the systemic immune response, elimination of regulatory T cells, and inhibition of tumor growth. To determine whether the combination of dendritic cells and anti‑GITR antibodies could enhance systemic immune responses and inhibit primary tumor growth in a murine osteosarcoma (LM8) model. We established the following 4 groups of C3H mice (20 mice in total): i), control IgG-treated mice; ii), tumor lysate-pulsed dendritic cell‑treated mice; iii), agonist anti-GITR antibody-treated mice; and iv), agonist anti-GITR antibody- and tumor lysate-pulsed dendritic cell‑treated mice.The mice that received the agonist anti-GITR antibodies and tumor lysate-pulsed dendritic cells displayed inhibited primary growth, prolonged life time, reduced numbers of regulatory T lymphocytes in the spleen, elevated serum interferon-γ levels, increased number of CD8+ T lymphocytes. The mice that received combined therapy had reduced level of immunosuppressive cytokines in tumor tissue and serum. Combining agonist anti-GITR antibodies with tumor lysate-pulsed dendritic cells enhanced the systemic immune response. These findings provide further support for the continued development of agonist anti-GITR antibodies as an immunotherapeutic strategy for osteosarcoma. We suggest that our proposed immunotherapy could be developed further to improve osteosarcoma treatment.

Interleukin-4 affects the mature phenotype and function of rat bone marrow-derived dendritic cells

Granulocyte macrophage‑colony stimulating factor (GM‑CSF), and GM‑CSF plus interleukin‑4 (GM‑CSF + IL‑4) are two commonly‑used cytokine therapies for the generation of bone marrow‑derived dendritic cells (DCs). However, the mechanisms underlying IL‑4 involvement in DC generation and maturation remain unclear. In order to investigate the effect of IL‑4 on DC generation, DCs from rat bone marrow progenitors were generated using GM‑CSF, with and without IL‑4. GM‑CSF + IL‑4 DCs exhibited more mature phenotypes, and the levels of naïve allogeneic T cell stimulation were greater compared with GM‑CSF DCs. Phosphorylated signal transducer and activator of transcription 6 (p‑STAT6), the active form of STAT6, was expressed in GM‑CSF + IL‑4 DCs but not in GM‑CSF DCs. The present study demonstrated that IL‑4 influences DC morphology and immune function, and that this process may be associated with the activation of STAT6.

Helicobacter pylori inhibits dendritic cell maturation via interleukin-10-mediated activation of the signal transducer and activator of transcription 3 pathway

Helicobacter pylori infects the human gastric mucosa causing a chronic infection that is the primary risk factor for gastric cancer development. Recent studies demonstrate that H. pylori promotes tolerogenic dendritic cell (DC) development indicating that this bacterium evades the host immune response. However, the signaling pathways involved in modulating DC activation during infection remain unclear. Here, we report that H. pylori infection activated the signal transducer and activator of transcription 3 (STAT3) pathway in murine bone marrow-derived DCs (BMDCs) and splenic DCs isolated ex vivo. Isogenic cagA-, cagE-, vacA- and urease-mutants exhibited levels of phosphoSTAT3 that were comparable to in the wild-type (WT) parent strain. H. pylori-infected BMDCs produced increased immunosuppressive IL-10, which activated STAT3 in an autocrine/paracrine fashion. Neutralization of IL-10 prevented H. pylori-mediated STAT3 activation in both BMDCs and splenic DCs. In addition, anti-IL-10 treatment of infected H. pylori-BMDCs was associated with increased CD86 and MHC II expression and enhanced proinflammatory IL-1β cytokine secretion. Finally, increased CD86 and MHC II expression was detected in H. pylori-infected STAT3 knockout DCs when compared to WT controls. Together, these results demonstrate that H. pylori infection induces IL-10 secretion in DCs, which activates STAT3, thereby modulating DC maturation and reducing IL-1β secretion. These findings identify a host molecular mechanism by which H. pylori can manipulate the innate immune response to potentially favor chronic infection and promote carcinogenesis.

The potential of antigen and TriMix sonoporation using mRNA-loaded microbubbles for ultrasound-triggered cancer immunotherapy

Dendritic cell (DC)-based cancer vaccines, where the patient's own immune system is harnessed to target and destroy tumor tissue, have emerged as a potent therapeutic strategy. In the development of such DC vaccines, it is crucial to load the DCs with tumor antigens, and to simultaneously activate them to become more potent antigen-presenting cells. For this, we report on microbubbles, loaded with both antigen mRNA as well as immunomodulating TriMix mRNA, which can be used for the ultrasound-triggered transfection of DCs. In vivo experiments with in vitro sonoporated DCs show the effective induction of antigen-specific T cells, resulting in specific lysis of antigen-expressing cells. Especially in a therapeutic setting, sonoporation with TriMix has an important added value, resulting in a significant reduction of tumor outgrowth and a marked increase in overall survival. What is more, complete tumor regression was observed in 30% of the antigen+TriMix DC vaccinated animals, which also displayed long-term antigen-specific immunological memory. As a result, DC sonoporation using microbubbles loaded with a combination of antigen and TriMix mRNA can elicit powerful immune responses in vivo, and might serve as a potential tool for further in vivo DC vaccination applications.

Investigating TLR signaling responses in murine dendritic cells upon bacterial infection

Innate immune recognition of microbial components is critical for the onset of an appropriate immune response against invading pathogens, in particular by dendritic cells. Toll-like receptors (TLRs) are key in the detection of a variety of microbial stimuli.Here we focus on the methodology used to evaluate the role of TLRs in the process of dendritic cell response to bacterial intracellular infections, using bone marrow-derived dendritic cells (BMDCs) as a model system. This protocol describes how to access the level of activation of BMDCs using standard immunology and biochemistry approaches along with examination of infected cells by immunofluorescence microscopy.

Enhancement of antitumor immunity by combining anti-cytotoxic T lymphocyte antigen-4 antibodies and cryotreated tumor lysate-pulsed dendritic cells in murine osteosarcoma

Immunotherapy with tumor lysate-loaded dendritic cells (DCs) is one of the most promising strategies to induce antitumor immune responses. However, the antitumor activity of cytotoxic T cells may be restrained by their expression of the inhibitory T-cell coreceptor cytotoxic T lymphocyte antigen-4 (CTLA-4). By relieving this restraint, CTLA-4-blocking antibodies promote tumor rejection, but the full scope of their most suitable applications has yet to be fully determined. In the present study, we offer proof of a preclinical concept in a C3H mouse osteosarcoma (LM8) model that CTLA-4 blockade cooperates with cryotreated tumor lysate-pulsed DCs in a primary tumor to prevent the outgrowth of lung metastasis. To evaluate immune response activation, we established the following four groups of C3H mice (60 mice in total): i) control immunoglobulin G (IgG)-treated mice; ii) tumor lysate-pulsed DC-treated mice; iii) anti-CTLA-4 antibody-treated mice and iv) tumor lysate-pulsed DC- and anti-CTLA-4 antibody-treated mice. The mice that received the tumor lysate-pulsed DCs and anti-CTLA-4 antibody displayed reduced numbers of regulatory T lymphocytes and increased numbers of CD8+ T lymphocytes inside the metastatic tumor, inhibition of metastatic growth, a prolonged lifetime, reduced numbers of regulatory T lymphocytes in the spleen and high serum interferon-γ levels. Combining an anti-CTLA-4 antibody with tumor lysate-pulsed DCs enhanced the systemic immune response. To the best of our knowledge, these findings document for the first time an effect of the combination of tumor lysate-pulsed DCs and CTLA-4-blocking antibodies in osteosarcoma. We suggest that cryotreated tumor lysate-pulsed DCs, although insufficient on their own, may mediate the rejection of metastatic lesions and prevent recurrence of the disease when combined with CTLA-4 blockade in osteosarcoma patients in the clinical setting.

Bone marrow-derived dendritic cells

While much is understood about dendritic cells and their role in the immune system, the study of these cells is critical to gain a more complete understanding of their function. Dendritic cell isolation from mouse body tissues can be difficult and the number of cells isolated small. This protocol describes the growth of large number of dendritic cells from the culture of mouse bone marrow cells. The dendritic cells grown in culture facilitate experiments that may require large number of dendritic cells without great expense or use of large number of mice.

Anti-TGF-β antibody combined with dendritic cells produce antitumor effects in osteosarcoma

BACKGROUND

We previously reported the combination of tumor cryotreatment with dendritic cells to promote antitumor immunity. The effect of the combination treatment with dendritic cells and antitransforming growth factor-β (anti-TGF-β) antibody on the elimination of regulatory T cells and the inhibition of tumor growth was investigated.

QUESTIONS/PURPOSES

The effects of the combination treatment with dendritic cells and anti-TGF-β antibody on the enhancement of systemic immune responses and inhibition of metastatic tumor growth were investigated in a murine osteosarcoma (LM8) model.

MATERIALS AND METHODS

To evaluate activation of the immune response, we established the following three groups of C3H mice (60 mice total): (1) excision only; (2) tumor excision and administration of anti-TGF-β antibody; and (3) tumor excision and administration of dendritic cells exposed to cryotreated tumor lysates with anti-TGF-β antibody.

RESULTS

The mice that received dendritic cells exposed to cryotreated tumor lysates with anti-TGF-β antibody showed increased numbers of CD8(+) T lymphocytes, reduced regulatory T lymphocytes in the metastatic lesion, and inhibition of metastatic growth. The combined therapy group showed reduced numbers of regulatory T lymphocytes in the spleen and high serum interferon γ level.

CONCLUSIONS

The control of the inhibitory condition induced by regulatory T cells is important to improve the suppression of the cytotoxic lymphocytes. Combining dendritic cells with anti-TGF-β antibody enhanced the systemic immune response.

CLINICAL RELEVANCE

We suggest that our immunotherapy could be developed further to improve the treatment of osteosarcoma.

Efficient human cytomegalovirus reactivation is maturation dependent in the Langerhans dendritic cell lineage and can be studied using a CD14+ experimental latency model

Studies from a number of laboratories have shown that the myeloid lineage is prominent in human cytomegalovirus (HCMV) latency, reactivation, dissemination, and pathogenesis. Existing as a latent infection in CD34(+) progenitors and circulating CD14(+) monocytes, reactivation is observed upon differentiation to mature macrophage or dendritic cell (DC) phenotypes. Langerhans' cells (LCs) are a subset of periphery resident DCs that represent a DC population likely to encounter HCMV early during primary infection. Furthermore, we have previously shown that CD34(+) derived LCs are a site of HCMV reactivation ex vivo. Accordingly, we have utilized healthy-donor CD34(+) cells to study latency and reactivation of HCMV in LCs. However, the increasing difficulty acquiring healthy-donor CD34(+) cells--particularly from seropositive donors due to the screening regimens used--led us to investigate the use of CD14(+) monocytes to generate LCs. We show here that CD14(+) monocytes cultured with transforming growth factor β generate Langerin-positive DCs (MoLCs). Consistent with observations using CD34(+) derived LCs, only mature MoLCs were permissive for HCMV infection. The lytic infection of mature MoLCs is productive and results in a marked inhibition in the capacity of these cells to promote T cell proliferation. Pertinently, differentiation of experimentally latent monocytes to the MoLC phenotype promotes reactivation in a maturation and interleukin-6 (IL-6)-dependent manner. Intriguingly, however, IL-6-mediated effects were restricted to mature LCs, in contrast to observations with classical CD14(+) derived DCs. Consequently, elucidation of the molecular basis behind the differential response of the two DC subsets should further our understanding of the fundamental mechanisms important for reactivation.

Eosinophils regulate dendritic cells and Th2 pulmonary immune responses following allergen provocation

Reports have recently suggested that eosinophils have the potential to modulate allergen-dependent pulmonary immune responses. The studies presented expand these reports demonstrating in the mouse that eosinophils are required for the allergen-dependent Th2 pulmonary immune responses mediated by dendritic cells (DCs) and T lymphocytes. Specifically, the recruitment of peripheral eosinophils to the pulmonary lymphatic compartment(s) was required for the accumulation of myeloid DCs in draining lymph nodes and, in turn, Ag-specific T effector cell production. These effects on DCs and Ag-specific T cells did not require MHC class II expression on eosinophils, suggesting that these granulocytes have an accessory role as opposed to direct T cell stimulation. The data also showed that eosinophils uniquely suppress the DC-mediated production of Th17 and, to smaller degree, Th1 responses. The cumulative effect of these eosinophil-dependent immune mechanisms is to promote the Th2 polarization characteristic of the pulmonary microenvironment after allergen challenge.

SHIP-deficient dendritic cells, unlike wild type dendritic cells, suppress T cell proliferation via a nitric oxide-independent mechanism

BACKGROUND

Dendritic cells (DCs) not only play a crucial role in activating immune cells but also suppressing them. We recently investigated SHIP's role in murine DCs in terms of immune cell activation and found that TLR agonist-stimulated SHIP-/- GM-CSF-derived DCs (GM-DCs) were far less capable than wild type (WT, SHIP+/+) GM-DCs at activating T cell proliferation. This was most likely because SHIP-/- GM-DCs could not up-regulate MHCII and/or co-stimulatory receptors following TLR stimulation. However, the role of SHIP in DC-induced T cell suppression was not investigated.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we examined SHIP's role in DC-induced T cell suppression by co-culturing WT and SHIP-/- murine DCs, derived under different conditions or isolated from spleens, with αCD3+ αCD28 activated WT T cells and determined the relative suppressive abilities of the different DC subsets. We found that, in contrast to SHIP+/+ and -/- splenic or Flt3L-derived DCs, which do not suppress T cell proliferation in vitro, both SHIP+/+ and -/- GM-DCs were capable of potently suppressing T cell proliferation. However, WT GM-DC suppression appeared to be mediated, at least in part, by nitric oxide (NO) production while SHIP-/- GM-DCs expressed high levels of arginase 1 and did not produce NO. Following exhaustive studies to ascertain the mechanism of SHIP-/- DC-mediated suppression, we could conclude that cell-cell contact was required and the mechanism may be related to their relative immaturity, compared to SHIP+/+ GM-DCs.

CONCLUSIONS

These findings suggest that although both SHIP+/+ and -/- GM-DCs suppress T cell proliferation, the mechanism(s) employed are different. WT GM-DCs suppress, at least in part, via IFNγ-induced NO production while SHIP-/- GM-DCs do not produce NO and suppression can only be alleviated when contact is prevented.

Elucidating the contribution of the elemental composition of fetal calf serum to antigenic expression of primary human umbilical-vein endothelial cells in vitro

One of the major obstacles to obtaining human cells of a defined and reproducible standard suitable for use as medical therapies is the necessity for FCS (fetal calf serum) media augmentation in routine cell culture applications. FCS has become the supplement of choice for cell culture research, as it contains an array of proteins, growth factors and essential ions necessary for cellular viability and proliferation in vitro. It is, however, a potential route for the introduction of zoonotic pathogens and makes defining the cell culture milieu impossible in terms of reproducibility, as the precise composition of each batch of serum not only changes but is in fact extremely variable. The present study determined the magnitude of donor variations in terms of elemental composition of FCS and the effect these variations had on the expression of a group of proteins associated with the antigenicity of primary human umbilical-vein endothelial cells, using a combination of ICPMS (inductively coupled plasma MS) and flow cytometry. Statistically significant differences were demonstrated for a set of trace elements in FCS, with correlations made to variations in antigenic expression during culture. The findings question in detail the suitability of FCS for the in vitro supplementation of cultures of primary human cells due to the lack of reproducibility and modulations in protein expression when cultured in conjunction with sera from xenogeneic donors.

Effect of different factors on proliferation of antler cells, cultured in vitro

Antlers as a potential model for bone growth and development have become an object of rising interest. To elucidate processes explaining how antler growth is regulated, in vitro cultures have been established. However, until now, there has been no standard method to cultivate antler cells and in vitro results are often opposite to those reported in vivo. In addition, many factors which are often not taken into account under in vitro conditions may play an important role in the development of antler cells. In this study we investigated the effects of the antler growth stage, the male individuality, passaged versus primary cultures and the effect of foetal calf serum concentrations on proliferative potential of mixed antler cell cultures in vitro, derived from regenerating antlers of red deer males (Cervus elaphus). The proliferation potential of antler cells was measured by incorporation of (3)H thymidine. Our results demonstrate that there is no significant effect of the antler growth stage, whereas male individuality and all other examined factors significantly affected antler cell proliferation. Furthermore, our results suggest that primary cultures may better represent in vivo conditions and processes occurring in regenerating antlers. In conclusion, before all main factors affecting antler cell proliferation in vitro will be satisfactorily investigated, results of in vitro studies focused on hormonal regulation of antler growth should be taken with extreme caution.

Dendritic cell-based vaccines for the therapy of experimental tumors

Dendritic cells (DCs) are believed to be the most potent antigen-presenting cells able to link the innate and adaptive immune systems. Many studies have focused on different immunotherapeutic approaches to applying DCs as tools to improve anticancer therapy. Although a number of investigations suggesting the benefit of DC-based vaccination during anticancer therapy have been reported, the general knowledge regarding the ultimate methods of DC-vaccine preparation is still unsatisfactory. In this article, the perspectives of DC-based anti-tumor immunotherapy and optimizing strategies of DC vaccination in humans in light of results obtained in mouse models are discussed.

Cryoimmunologic antitumor effects enhanced by dendritic cells in osteosarcoma

BACKGROUND

We previously reported a limb-salvage technique by treating tumor-bearing bone with liquid nitrogen. We also reported systemic antitumor immunity was enhanced by cryotreatment in a murine osteosarcoma (LM8) model. We therefore combined the cryotreatment of tumor with dendritic cells to promote tumor-specific immune responses.

QUESTIONS/PURPOSES

We determined whether our technique could enhance systemic immune response and inhibit metastatic tumor growth in a murine osteosarcoma model.

MATERIALS AND METHODS

To evaluate activation of the immune response, we prepared six groups of C3H mice (80 mice total): (1) excision only, (2) dendritic cells without reimplantation of the cryotreated primary tumor, (3) reimplantation of the cryotreated primary tumor alone, (4) dendritic cells combined with reimplantation of the cryotreated primary tumor, (5) dendritic cells exposed to cryotreated tumor lysates without reimplantation of the cryotreated primary tumor, and (6) dendritic cells exposed to cryotreated tumor lysates with reimplantation of the cryotreated primary tumor. We then compared and verified the activation state of each group's antitumor immunity.

RESULTS

Mice that received dendritic cells exposed to cryotreated tumor lysates with reimplantation of the cryotreated primary tumor group had high serum interferon gamma, reduced pulmonary metastases, and increased numbers of CD8(+) T lymphocytes in the metastatic areas.

CONCLUSIONS

Combining tumor cryotreatment with dendritic cells enhanced systemic immune responses and inhibited metastatic tumor growth.

CLINICAL RELEVANCE

We suggest immunotherapy could be developed further to improve the treatment of osteosarcoma.

Choosing and preparing antigen-presenting cells

The first issue in selecting a system for antigen-presentation experiments is to define the appropriate type of antigen-presenting cell (APC) to study. For some experiments, crude preparations such as splenocytes or peripheral blood mononuclear cells (PBMCs) may suffice to provide APC function for stimulating T cells. This unit develops approaches for preparation of more defined APC populations, including dendritic cells (DCs), macrophages, and B lymphocytes, the three types of "professional" APC. Each of these cell types exists in different stages of differentiation, maturation, and activation, or in some cases different lineages. For example, dendritic cells may be divided into subsets, including myeloid DCs (mDCs) and plasmacytoid DCs (pDCs). Each APC type has an important antigen-presentation function, although they contribute to different aspects of the immune response. Therefore, selection of an APC type for study must include consideration of the stage or aspect of immune response that is to be modeled in the experiment.

Preparation of mouse bone marrow-derived dendritic cells with immunoregulatory properties

Tolerogenic dendritic cells (Tol-DCs) are critical players in physiological tolerance. Moreover, they also play a role in immune regulation both in a pathophysiological context and when used as therapeutic tools in cell therapy strategies. Here, we describe a protocol to differentiate murine Tol-DCs from bone marrow precursors in vitro. Importantly, Tol-DCs actively suppress T cells stimulated with immunogenic allogeneic DCs. Indeed, Tol-DCs generated using this approach can be useful in studying and characterising the immunoregulatory pathways of Tol-DC and in developing Tol-DC-based cell therapy protocols using in vivo models.

A defined serum-free medium useful for monitoring anti-melanoma responses induced by dendritic cell immunotherapy

Animal sera provide a non-defined source of nutrients and growth factors for mammalian cell culture. Animal serum supplementation may also introduce experimental artefacts, including immune responses against foreign serum proteins. This artefact is particularly apparent in tumour immunotherapy experiments using dendritic cells (DC) and melanoma cells cultured in fetal calf serum (FCS)-replete media. FCS culture of both DC and melanoma cells significantly enhanced anti-tumour responses in mice immunized with DC that had not been pulsed with tumour antigen. Although serum-free media (SFM) may be used for short term culture of cells, most SFM do not support long term culture of tumour cell lines. In addition, in vivo propagation and re-isolation of tumour cells from rodents is expensive, time consuming and only low numbers of viable tumour cells can be recovered from solid tumours. We show that a defined SFM medium is ideal for routine culture of B16 for use in prophylactic DC immunizations, negating the need for in vivo propagation of tumours to avoid FCS effects in tumour implantation experiments.

Minor role of bystander tolerance to fetal calf serum in a peptide-specific dendritic cell vaccine model against autoimmunity: comparison with serum-free cultures

Dendritic cells (DCs) are currently considered as promising tools for vaccination against tumors and also autoimmune responses. A major point of concern has been the use of fetal calf serum (FCS) as a source of heterologous antigen in DC cultures. FCS peptides can be presented by the DCs and cause T-cell responses in the recipient. We investigated the role of FCS in an autoimmune model where DC injections can prevent peptide-specifically from experimental autoimmune encephalomyelitis (EAE). We show that murine bone marrow-derived DCs generated in FCS-containing or serum-free media resulting in a similar phenotype, maturation potential, and functions. Peptide-specific protection could be achieved similarly with FCS-DC or serum-free DCs. Although FCS-DC induced strong CD4 T cell proliferation and cytokine production against FCS, these T cells lack antigenic recall during EAE. Even if FCS was reinjected, the effect on EAE resulted only in a 3-day delay of disease onset. Together, our data show that presentation of bystander antigens by peptide-specific DC vaccinations may have little influence on T-cell responses in vivo if the bystander antigen cannot be recalled by specific T cells.